This invention relates to projectiles for use in round bore electromagnetic projectile launchers and more particularly to such projectiles which include structures that are used to electromagnetically produce or prevent projectile spin.
Parallel rail electromagnetic projectile launchers include a pair of generally parallel conductive rails, a plasma or sliding conductive armature for conducting current between the rails, a source of high current, and means for commutating this current into the rails and the armature. This flow of current places an electromagnetic force on the armature which propels it along the conductive rails.
Common methods of stabilizing projectiles include the use of stabilizing fins on the projectiles or the use of a rifled barrel assembly. These methods provide spin stabilization which is desirable in many launcher applications. However, there are certain applications, such as where independently guided projectiles are used, wherein projectile spin is to be avoided. Such independently guided projectiles are commonly referred to as "smart" projectiles.
One common electromagnetic launcher construction includes parallel-sided rails which require that at least a portion of the projectile or the associated armature has a rectangular cross section. This essentially precludes imparting rotation to the projectile for spin stabilization. If projectile spin is desired, it must be imparted by separate means such as fins attached to the projectile. Spin stabilization can also be achieved by providing the launcher with skewed conductive rails which cause the projectile to spin by making the armature lock-step with the rails. This introduces additional complexity in the rail design. In addition, slotted coaxial electromagnetic launchers have been proposed which also introduce manufacturing complexities.
Electromagnetic launcher barrels experience forces similar to those of conventional guns. Since such barrels can be made of several sections, these forces make it difficult to successfully introduce rifling for projectile spin stabilization. Where the barrels are segmented, the rifling grooves must not only be consistent in a single section of barrel, but must also be continuous between separate barrel segments. It is therefore desirable to design a projectile which can be spin stabilized without the need for a rifled barrel.
One such spin stabilization method is illustrated in U.S. Pat. No. 4,449,441, issued May 22, l984 to McAllister. That patent discloses a round bore electromagnetic launcher wherein spin stabilization of a projectile is accomplished through the use of a spin-producing magnetic flux field near the muzzle section of the launcher. To accomplish spin stabilization, the projectile is provided with a cage winding or a magnetic segment having skewed notches, which interact with the spin-producing magnetic flux to impart spin to the projectile.